The "file tree" is currently rendered mostly on the server, and has a preference to enable or disable it. I think the preference was originally motivated by performance concerns.

In modern Phabricator, the performance cost of the file tree is likely no longer very significant compared to all the other things the page is doing. This preference can probably be removed. Note that the file tree can still be expensive on large changes (PHI485 has a profile where it took 3s to render on a 3,500 file change, and likely provides little or no value) and should degrade.

Right now, the file tree has a significant server-side component. This probably makes sense to move to the client.

See also PHI485, which would like to sort "files affecting packages I own" to the top. We could let you sort (and even drag) files using the file tree, although this feels highly ambitious.

Done

• Previously, see T13110.
• After the "buoyant header" is painted, the formation view should repaint.
• See PHI595, which would like better accessibility hints in the filetree.
• See PHI356. When a change affects a/b/c/d.txt but no other files under a/, a single directory entity a/b/c can be rendered.
• See PHI356. Package authority could reasonably be shown in the filetree.
• See also T7467 ("render deleted files more prominently").
• See T13455. At the file level, "collapsed" should be shown in the tree UI. The "disclosure triangle" for a given file could be a toggle for the collapse option.
  • (For now, not planning to provide a direct collapse action from the file tree for paths -- selection behavior is better and you can press "h" after clicking, plus screen real estate is tight.)
• See PHI1551. Keyboard navigation allows you to "select" a file, which is a different concept from "currently visible file" in the file tree. This isn't communicated clearly. The banner "selection" state may also differ from the filetree "selection" state. They should always select the same file. "Collapse File" should have the same targeting rules as "Open in Editor".
• See PHI1257. Putting page navigation anchors (Comment, Table of Contents) into the file tree might be helpful.
• If you toggle flank visibility with an active diff selection, the reticle does not redraw properly.
  • (More or less "fixed" by changing what the reticle looks like.)
• When you jump to a file via clicking or "N/P", we should history-push the page URI.
  • (Not actually going to do this, I think it'll be more distracting than useful.)
• Celerity package definitions should be updated.
• The formation column should be hidden on mobile.
• The global footer is bleeding into the flank nav.